Abstract
This paper presents a novel method employing the maximum likelihood estimation (MLE) technique alongside a nonlinear sensor response model to improve and extract more quantitative sensing results for localized surface plasmon resonance biosensors. The nonlinear response model treats the sensor response as a nonlinear function of the biomolecular adlayer thickness. This method makes use of the multiple resonance characteristic of nanocrescent structures in order to estimate the adlayer thickness and bulk refractive index (RI) change. Nanoimprint lithography is used here to fabricate the nanostructures. The finite element method (FEM) is used to model the nanocrescents and numerically validate the nonlinear-MLE method. Comparing to the established linear model, the proposed nonlinear-MLE method achieves 75% improvement in the limit of detection based on the estimated adlayer thickness and improves the bulk RI resolution by two orders of magnitude.
Highlights
Localized Surface Plasmon Resonance (LSPR) biosensors have been of interest in sensing applications due to their plasmonic properties, small size and small sample requirement
The sensor response–at each resonance–is related to the adlayer thickness and bulk refractive index (RI) changes,and the effects can be determined by solving the two equations. This linear response model has been previously employed for an SPR sensor with a dielectric overlayer to excite two resonances[10], an SPR sensor based on simultaneous excitation of short and long range SPR modes[11,12], a dual-resonance SPR sensor with different penetration depths[13], simultaneous excitation of transverse and longitudinal modes of nanorods[14], and a sensor based on surface plasmon resonance and plasmon waveguide resonance[15]
This section compares the nonlinear–maximum likelihood estimation (MLE) method with the established linear response model based on finite element method (FEM) simulated results, and presents a FEM evaluation for the accuracy based on each method with respect to deviated resonance wavelengths
Summary
Localized Surface Plasmon Resonance (LSPR) biosensors have been of interest in sensing applications due to their plasmonic properties, small size and small sample requirement. This linear response model has been previously employed for an SPR sensor with a dielectric overlayer to excite two resonances[10], an SPR sensor based on simultaneous excitation of short and long range SPR modes[11,12], a dual-resonance SPR sensor with different penetration depths[13], simultaneous excitation of transverse and longitudinal modes of nanorods[14], and a sensor based on surface plasmon resonance and plasmon waveguide resonance[15] This model, requires a sensitivity matrix (including the adlayer and bulk RI sensitivities for both resonances) with a low condition number to avoid any numerical errors, which may not be the case for many sensing platforms.
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